-LRB- CNN -RRB- -- To control costs and increase flexibility , more and more U.S. mobile users are choosing no-contract plans -LRB- month-to-month or prepaid -RRB- for cell phone service .

How happy are consumers with no-contract phones and service ? J.D. Power and Associates recently released the results of its 2011 U.S. Wireless Non-Contract Customer Satisfaction Index Study . The no-contract carriers studied were : AT&T Gophone , Boost Mobile , Cricket , MetroPCS , Net10 , T-Mobile , Tracfone , Verizon Wireless and Virgin Mobile .

This year , the overall winner was Boost Mobile , which scored top marks for its cost of service , account management practices , initial activation process and offers/promotions . However , Boost scored only a middling grade on performance and reliability , the characteristic that survey participants rated as most important .

Net10 , Tracfone , and Verizon Wireless received consumers ' highest ratings for performance and reliability ; while AT&T Gophone , Cricket and MetroPCS fared worst on this front .

AT&T Gophone received the overall worst customer satisfaction rating this year , with poor to middling marks in all categories .

According to Valassis , a media and marketing services company , as of October of last year , 28 % of all U.S. cell phone service plans did not have contracts -LRB- up from 21 % in 2008 -RRB- . Meanwhile , J.D. Powers reports that this year , about half of of all no-contract customers have month-to-month plans , rather than prepaid ones . In 2008 , only 30 % of no-contract plans were monthly .

The increase in attractive monthly no-contract offers might start stealing customers away from contracts . J.D. Powers notes : `` Among customers currently under -LSB- a regular carrier contract of a year or more -RSB- and who say they are likely to switch their carrier during the next year , nearly 40 percent are likely to choose non-contract service . ''

Monthly contracts are generally cheaper . According to J.D. Powers : `` Monthly non-contract customers spend an average of $ 32 less per month than do customers with contracts . Monthly non-contract customers spend $ 60 per month , compared with an average monthly service cost of $ 92 for customers with service contracts . ''

Some smartphones are now available on no-contract plans . Most no-contract carriers offer some smartphone deals -- usually for BlackBerry phones , but increasingly for Android and some Windows Phone models , too .

These smartphones still cost substantially more to buy up front than the simpler , cheaper `` feature phones '' these carriers mostly offer , and they generally do n't have the latest or most robust technology or operating system versions . Whether these offerings will entice many first-time smartphone buyers remains to be seen .

For example , MetroPCS currently offers a no-contract Huawei Ascend touchscreen phone running Android 2.1 for $ 129 after a $ 50 instant discount and $ 30 mail-in rebate ; the month-to-month plan cost is $ 50 . Similarly , Virgin Mobile is currently offering the LG Optimus -LRB- running Android 2.2 -RRB- and Samsung Intercept -LRB- running Android 2.1 -RRB- for $ 199.99 , with month-to-month plans starting at $ 25 .

Right now , the major U.S. wireless carriers are making considerable revenue off of smartphone customers under two-year contracts . And so far , it 's pretty hard to get a higher-end smartphone without a two-year contract in the U.S. .

But lower-end smartphones might suffice for many mobile users . That 's why offers such as these could alter the U.S. wireless competitive landscape over the next few years .

The opinions expressed in this post are solely those of Amy Gahran .

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Boost Mobile scored top marks overall among owners of no-contract phones

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Among no-contract carriers , AT&T Gophone got the lowest customer satisfaction rating

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A few smartphones are now available on no-contract plans